Information carrier, reading/writing device and reading device for writing and/or reading information blocks

ABSTRACT

A disc-shaped information carrier and a device for reading and/or writing information blocks in a track thereon which follows a helical or concentric path forming successive windings. For identifying each winding the information carrier also has a servo pattern thereon which includes position-information as well as synchronization elements. Such elements may be, for example, brief pulses in a continuous track wobble, and are distinguishable in adjacent windings based on a predetermined detectable parameter, such as alternating polarity or shifted relative phase positions. The device has a read/write head and a system control which during writing detects the synchronization elements and monitors whether a deviation has occurred signifying that the read/write head has wandered to an adjacent winding. In that event writing is interrupted. Thus, the least possible information in adjacent windings is overwritten in the case of disturbances resulting from shocks or defects of the information carrier. A read device is also described which interrupts reading if the winding identification provided by the synchronization elements signifies erroneous operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an information carrier for writing and/orreading information blocks in/from a track intended for recording andarranged in a helical or concentric pattern of windings, the track beingdetermined by a servo pattern on the information carrier, the servopattern comprising synchronization elements and a modulation, in whichmodulation position-information is coded.

The invention further relates to a reading/writing device comprisingreading/writing means for reading and/or writing information blocksfrom/in an information carrier track intended for recording, the trackbeing arranged in a helical or concentric pattern of windings, anddetermined by a servo pattern on the information carrier. The servopattern comprises synchronization elements and is modulated with codedposition-information. The device has a read/write head for scanning thetrack and a system control for controlling the scanning in dependence onthe synchronization elements.

The invention further relates to a reading device comprising readingmeans for reading information blocks from a track on an informationcarrier, the track being arranged in a helical or concentric pattern ofwindings and the track being determined by a servo pattern on theinformation carrier, the servo pattern comprising synchronizationelements, the device comprising a read head for scanning the track and asystem control for controlling the scanning.

2. Description of the Related Art

An information carrier and a device of the type defined in the openingparagraph for reading and/or writing information thereon are known fromU.S. Pat. No. 4,901,300 issued Feb. 13, 1990, assigned to Philips. Theinformation is coded to form an information signal which may besubdivided into addressable information blocks as on a CD-ROM. Theinformation carrier has a pregroove for producing tracking servosignals, the radial position of which pregroove periodically varies in aso-termed wobble. The device comprises a read/write head for scanningthe track. During the scanning, this wobble causes a modulation of thetracking servo signals. This modulation comprises code modulationsynchronization elements and position-information whichposition-information denotes the absolute length of the track from thestarting point. The information blocks are recorded on the informationcarrier at a desired position that corresponds to their address, theposition of the read/write head in the track being derived from theposition-information. The writing of the information blocks issynchronized with the synchronization symbols.

A problem for such a system is that the read/write head may wander offthe track and cause information in an adjacent track to be destroyed asa result of a defect or a shock during writing.

SUMMARY OF THE INVENTION

It is an object of the invention, to provide detection means fordetecting in an easy and rapid fashion whether the read/write head haswandered off the track. For this purpose, an information carrieraccording to the invention is characterized in that the synchronizationelements in adjacent windings can be distinguished in a predeterminedmanner. Thereto, a reading/writing device according to the invention ischaracterized in that, while the synchronization elements (35, 36) inadjacent windings are predeterminably distinguishable, the systemcontrol (46) is arranged for distinguishing synchronization elements(35, 36) of an adjacent winding if the adjacent winding is erroneouslyscanned during the writing of an information block, and for interruptingthe writing if such erroneous scanning takes place. The invention isadvantageous, for example, in that destruction of information in anadjacent track is limited. A reading device according to the inventionis characterized in that, while the synchronization elements (35, 36) inadjacent windings are predeterminably distinguishable, the systemcontrol (46) is arranged for distinguishing synchronization elements(35, 36) of an adjacent winding if that winding is erroneously scannedduring the reading of an information block, and for interrupting thereading if such erroneous scanning takes place. This is advantageous inthat the reading of unwanted information is restricted.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIGS. 1a-1d show an information carrier which has a servo pattern,

FIG. 2 shows a land/groove servo pattern,

FIGS. 3A-3C show a modulation in adjacent windings,

FIG. 4 shows a reading/writing device for reading and/or writinginformation blocks; and

FIG. 5 shows a reading device.

Figure elements corresponding to elements already described carry likereference characters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1a shows a disc-shaped information carrier 1 having a track 9intended for recording, which track is arranged in a helical pattern ofwindings 3. The windings may also be arranged concentrically instead ofhelically. The track 9 on the information carrier is indicated by aservo pattern such as, for example, a pregroove 4 which enables aread/write head to follow the track 9 during scanning. A servo patternmay also be formed, for example, by regularly spread sub-patterns which,in the servo tracking system, periodically cause tracking signals tooccur. FIG. 1b shows a cross-section along a line b--b of theinformation carrier 1, in which a transparent substrate 5 is covered bya recording layer 6 and a protective layer 7. The pregroove 4 may alsobe arranged as a land or other material property that differs from itsenvironment. Furthermore, the servo pattern may also be formed byalternately raised and depressed windings, forming so-called land andgroove patterns, with a transition from land to groove or vice versa ineach winding. The recording layer 6 can be written optically,magneto-optically or magnetically by an apparatus for reading and/orwriting information such as the known CD Recordable or hard disk forcomputer use. The FIGS. 1c and 1d show two examples of a periodicmodulation (wobble) of the pregroove. This wobble causes an additionalsignal to arise in a servo tracking detector. The wobble is, forexample, frequency modulated and in the modulation position-informationis coded, such as an address or a tine code. A description of aninscribable CD system comprising position-information obtained in suchmanner can be found in U.S. Pat. No. 4,901,300 (PHN 12398) and U.S. Pat.No. 5,187,699 (PHQ 88002), both assigned to Philips. Another example ofposition-information modulation are header symbols included in the servopattern, which header symbols are indicative of an address and indicatethe beginning of the area for recording an information block.

FIG. 2 shows a land/groove pattern in which a wobble 21 is introduced onone side in which, for example, from the inside out (from the bottom upin FIG. 2) a land/groove (L/G) transition is straight and a groove/land(G/L) transition shows a wobble. The same wobble signal is thendeveloped in land and groove, but since it is also known whether a landor a groove is scanned, the winding can be determined unambiguously.

On the information carrier according to the invention, windings 3 in thearea intended for recording contain winding information which indicates,for example, the radial position of the winding such as, for example awinding number and/or sector addresses. A winding number, for example,counts up from 0 from the innermost winding outward. The windinginformation may also denote a distance to the center of rotation. Fordecoding the winding information, it is advantageous for the modulationof the pregroove to have a pattern such that a constant frequencyevolves during reading, irrespective of the radial position. With asimple filter it is possible to separate well a modulated signal havinga constant frequency from noise signals. For this purpose, the period ofthe space modulation preferably increases proportionally with thedistance to the center of rotation 10. As a result, a constant angularvelocity of the information carrier produces to a constant modulationfrequency. Alternatively, another pattern of the space modulation periodand a linked pattern of the angular velocity may be selected. Forverifying the exact winding after a jump, it is advantageous for thewinding information to be repeated several times per winding in windinginformation frames. Such winding information frames are to be decodableindependently. This also provides a good protection against localdamage. It is advantageous to number the winding information framessequentially with segment numbers, so that always an indication isavailable of the angular position relative to the reference line 8,where the winding numbers increase for a helical track, or where thetransitions take place at a land/groove.

FIGS. 3A-3C diagrammatically show the modulation of a servo patternaccording to the invention. This modulation may be realized as pregroovewobble on the information carrier as described in FIG. 1. The modulation30, 31 is shown in two adjacent windings N and N+1 (or winding pairs inthe case of L/G shown in FIG. 2). The modulation has a wobble 32 with arelatively long period and has synchronization elements 35, 36, 37, 38,39, 40 with a relatively short period. The amplitude of thesynchronization elements is also larger than the amplitude of the wobble32. This is advantageous in that the synchronization elements are easyto detect. The synchronization elements may also be modulated in adifferent manner, such as, for example, a phase jump in the wobble. Thesynchronization elements may be used for synchronizing the writingand/or reading, such as controlling the rotation or scanning velocity ofthe information carrier, inserting the information blocks in the trackat a precisely determined position on the information carrier, orreading the position-information from the wobble of the servo pattern.The combination of the wobble and the synchronization elements permitsinformation to be recorded in blocks in a simple manner, even ifinformation has already been recorded in track where the new informationis to join.

FIG. 3a shows an embodiment of the invention in which thesynchronization elements in adjacent tracks always have an alternatingpolarity. The synchronization elements 35 in the winding N continue tohave the same, for example, positive polarity, whereas thesynchronization elements 36 in the adjacent winding N+1 always have adifferent, for example, negative polarity. Obviously, this pattern isrepeated, so that track N-1 is again equal to track N+1. Thesynchronization elements 37 in the winding N in FIG. 3b have an everalternating polarity, whereas the corresponding synchronization elements38 in the adjacent winding N+1 always have the different, oppositepolarity. In the embodiment shown in FIGS. 3a and 3b, thesynchronization elements in adjacent windings are always aligned. FIG.3c shows a fixed shift between adjacent windings over half the distancebetween synchronization elements in lieu of aligned synchronizationelements. In that case, the detection of the winding jump can be derivedfrom the instant at which a synchronization element is read. This isadvantageous in that an error is established more rapidly for an equalnumber of synchronization elements (as a result of the lack of or earlyappearance of a synchronization element). If, for example, one third ofthe distance is considered a shift, it is also possible to detect anundesired jump over two windings. Obviously, further patterns of shiftsare possible, possibly combined with the use of various types ofsynchronization elements. Alternatively, a different number ofsynchronization elements (and thus a different distance between them)may be used per winding. In lieu of the different polarities, it is alsopossible to use various types of synchronization elements whichcomprise, for example, two short and two long pulses in differentsequences.

With the above different synchronization elements, distances and shiftsit is possible to form a recurrent pattern of distinguishabledifferences over the number of tracks, by which also an undesireddisplacement over various tracks and/or the direction of thedisplacement can be detected.

While such an information carrier according to the invention is beingwritten, it is easy to detect whether a read/write head is positionedover the correct track or over an adjacent track. Since always theinstant and the polarity of the next synchronization element is known,an undesired jump to an adjacent winding can be detected when anerroneous synchronization element is found. The writing operation canthen be interrupted immediately so as to damage the least possible datain an adjacent winding by overwriting. A next synchronization elementmay be waited for, and the writing will not be interrupted until after arecurrent error. It is also possible to combine the detected informationwith information from the servo system in which system often track-lossinformation can also be derived. Combining servo track-loss informationwith synchronization element detection information enhances thereliability of the detection of undesired displacements of theread/write head.

The synchronization elements are desirably recorded in the servo patternat regular intervals. This provides a relatively fast detection of anundesired displacement of the read/write head. Preferably, the mutualdistance of synchronization elements in adjacent tracks is smaller thanthe length of an information block, so that at most this distance can beoverwritten erroneously. In a reading/writing system in which theinformation is protected by an error correction code, the maximum lengthof the track that can be written erroneously is desirably selectedsmaller than the maximum burst error to be corrected. The distancebetween the synchronization elements and the number of erroneousdetections thereof necessary for interrupting the writing operation canbe adjusted to this.

It is observed that the pattern of synchronization elements per windingof a helical track may differ. At a certain angular position, there willthus be an exchange of patterns as denoted along the imaginary line 8 inFIG. 1a.

FIG. 4 shows a device for writing and reading information blocks on adisc-shaped information carrier which can be written magneto-opticallyor optically (via phase change). The device comprises drive means 45 forcausing the information carrier to rotate and a read/write head 42 forscanning the track indicated on the information carrier by the servopattern. The read/write head 42 is positioned on the track in radialdirection by servo control unit 44. The read/write head scans the trackwith known tracking and focusing methods and a modulation caused, forexample, by the wobble in the pregroove is present in the servo signals.The servo signal is demodulated and the position-information codedtherein is recovered in the servo control unit 44 and passed on to thesystem control 46. The radial position of the read/write head may bechecked via the recovered position-information. The information appliedto the input of the coding unit 41 is divided into blocks, as required,and converted into a writing signal for the read/write head 42. Thecoding unit 41 comprise, for example, an error coder and channel coder.During the reading operation, the signal from the read/write head 42 isreconverted into the information in the decoding unit 43 comprising, forexample, a channel decoder and an error corrector. The device comprisesa synchronization unit 47 for synchronizing the writing and readingoperations. The timing of the writing is then customarily controlled independence on the recovered synchronization elements. The system control46 controls the synchronization unit 47 and, in addition, the servocontrol 44, the coding unit 41, the decoding unit 43 and the drive means45 and is arranged for executing the procedures to be describedhereinafter.

When an information carrier 1 has been inserted into the device and awriting instruction has been received, the system control 46 positionsthe read/write head 42 over the desired winding and the writing isstarted at the correct instant, for example, synchronized with a firstsynchronization element. The pattern of the synchronization elements inthe track to be written is known, however. The system control isarranged according to the invention for detecting a secondsynchronization element of a certain type and/or a synchronizationelement at a certain moment, and subsequently, further synchronizationelements. However, if a synchronization element or a wrong type ofsynchronization element is detected at another instant that means thatthe read/write head 42 has wandered off to an adjacent winding as aresult of a shock or a defect, and the system control will interrupt thewriting operation. An example of a pattern of aligned synchronizationelements in adjacent windings is shown in FIG. 3b. The polarity of thesuccessive synchronization elements in the track to be written thenalternates. If the system control detects the same polarity twice insucession, that signifies that the read/write head has wandered off toan adjacent winding.

FIG. 3c shows a pattern of shifted synchronization elements. If thesystem control 46 detects a synchronization element too early, or doesnot find a synchronization element at the expected instant, that meansthat the read/write head has wandered off to an adjacent track. When,for example, 4 different types of synchronization elements are used in apattern which recurs every 4 windings, the system control will detectthe error even with an undesired displacement over a maximum of 3windings, because it detects an unexpected type. In an embodiment of thesystem control the writing will not be stopped until the second orfurther unexpectedly detected synchronization elements has occurred.This is advantageous in that a single synchronization elementerroneously detected as faulty does not immediately lead to aninterruption of the writing process. A further embodiment of the systemcontrol also evaluates the servo signals and derives therefrominformation about track loss in known manner. This information may becombined with the unexpectedly detected synchronization elements. Adecision to interrupt may then be made both in the case of a track lossindication and an erroneous synchronization element. This isadvantageous in that the reliability of the decision is enhanced,because the two indications are formed independently.

FIG. 5 shows a reading device according to the invention by which aninformation block can be similarly read. The reading device comprisesdrive means 45 for causing the information carrier 1 to rotate and aread head 52 for scanning the track on the information carrier. The readhead 52 is positioned in radial direction on the track by servo meanscontrol unit 44. Furthermore, the device comprises a system control 46.During the reading operation, the signal from the read head 52 isconverted into the information in the decoder unit 43 which comprises,for example, a channel decoder and an error corrector. In the embodimentaccording to the invention, the system control 46 detects thesynchronization elements during the reading operation. In the event of adeviation, the reading may be interrupted. A control signal may be sentto the servo control unit 44, as required, so that a jump is made backin the direction of the desired winding, provided that this directioncan be derived from the detected synchronization element (the pattern isdifferent over more than 2 adjacent windings) and/or from the variationof the servo signals. Furthermore, the system control can, after aninterruption, directly carry out a repetition and cause the desiredtrack to be read out once again.

We claim:
 1. A read/write device comprising means for reading and/orwriting information blocks on a recording track of an informationcarrier, which track follows a helical or concentric path formingsuccessive windings, the track path being determined by a servo patternon the information carrier; said servo pattern including: (i) amodulation of the track path in accordance with coded positioninformation, and (ii) periodic synchronization pulses, those in adjacenttrack windings being distinguished from each other by at least onepredetermined detectable parameter thereof; said device comprising:aread/write head (42) for scanning the track; and a system controlarrangement (46, 47) for controlling the read/write head in accordancewith the synchronizing pulses in the servo pattern; the system controlarrangement being adapted to distinguish the synchronization elements ofan adjacent track winding if such winding is scanned erroneously duringwriting of an information block on another track winding, and in thatevent to interrupt writing of information during said erroneous scanningof an adjacent track winding.
 2. A read/write device as claimed in claim1, wherein the synchronization pulses in adjacent track windings aredistinguishable from each other by a plurality of predetermineddetectable parameters thereof, and the system control arrangement isadapted to distinguish between the synchronization pulses of adjacentwindings bas ed on said parameters.
 3. A read/write device as claimed inclaim 1, wherein the synchronization elements in adjacent windings havepredetermined phases relative to each other, and the system controlarrangement is adapted to distinguish the relative phases of thesynchronization pulses during writing of information blocks on therecording track.
 4. A read/write device as claimed in claim 1, whereinthe synchronization pulses in adjacent windings have opposite relativepolarities and the system control arrangement is adapted to distinguishbetween said windings based on said polarities during writing ofinformation blocks on the recording track.
 5. A read/write device asclaimed in claim 1, wherein the synchronization pulses in adjacentwindings are concurrent in time but differ in a predetermined parameterthereof, and the system control arrangement is adapted to distinguish,during writing of information blocks on the recording track, deviationsof said parameter from a condition thereof which is produced when anintended track winding is being scanned.
 6. A read/write device asclaimed in claim 1, therein the synchronization pulses in adjacentwindings have different relative phase positions with respect to thetrack modulation, and the system control arrangement is adapted todistinguish between synchronization pulses of adjacent windings based onlengths of the periods of track modulation between successivesynchronization pulses.
 7. A read device comprising means for readinginformation blocks recorded on a recording track of an informationcarrier, which track follows a helical or concentric path formingsuccessive windings, the track path being determined by a servo patternon the information carrier; said servo pattern including: (i) amodulation of the track path in accordance with coded positioninformation, and (ii) periodic synchronization pulses, those in adjacenttrack windings being distinguished from each other by at least onepredetermined parameter thereof; said device comprising:a read head (52)for scanning the track; and a system control (46) for controlling theread head in accordance with the synchronization pulses in the servopattern; the system control being adapted to distinguish thesynchronization pulses of an adjacent track winding if such winding iserroneously scanned during reading of an information block from anothertrack winding, and in that event to interrupt reading during saiderroneous scanning of an adjacent track winding.
 8. An informationcarrier having a recording track which follows a helical or concentricpath forming successive windings and which is adapted to haveinformation recorded thereon in the form of successive informationblocks, the track path being determined by a servo pattern on theinformation carrier;said servo pattern comprising:(i) a modulation of apredetermined detectable physical characteristic of the track path inaccordance with coded position information, and (ii) periodicsynchronization pulses, those in adjacent track windings beingdistinguished from each other based on a difference in the relativepolarities of said pulses.
 9. An information carrier having a recordingtrack which follows a helical or concentric path forming successivewindings and which is adapted to have information recorded thereon inthe form of successive information blocks, the track path beingdetermined by a servo pattern on the information carrier;said servopattern comprising:(i) a modulation of a predetermined detectablephysical characteristic of the track path in accordance with codedposition information, and (ii) periodic synchronization pulses, those inadjacent track windings being distinguished from each other based on adifference in the relative phases of said pulses.
 10. An informationcarrier having a recording track which follows a helical or concentricpath forming successive windings and which is adapted to haveinformation recorded thereon in the form of successive informationblocks, the track path being determined by a servo pattern on theinformation carrier;said servo pattern comprising:(i) a modulation of apredetermined detectable physical characteristic of the track path inaccordance with coded position information, and (ii) periodicsynchronization pulses, those in adjacent track windings beingdistinguished from each other by opposite relative polarities.